Scaling and corrosion resistant fluid conduit

ABSTRACT

A fluid conduit (10) is provided having (a) a fluid conduit exterior surface (14); (b) a fluid conduit interior surface (16); (c) an electroless nickel protective coating (18) disposed upon one or both of the fluid conduit interior surface and the fluid conduit exterior surface; and (d) a layer (20) of Ni3S2 disposed upon and substantially covering the electroless nickel protective coating. The fluid conduit can be any fluid conduit through which a fluid may be caused to pass, such as a downhole tubular used in oil and gas production, or a gas liquid cyclonic separator. And a hydrocarbon production tube, a method of producing a fluid conduit comprising a nickel sulfide protective layer, a machine component comprising at least one surface having a protective outer layer are provided. The combination of the electroless nickel inner protective coating with an outer layer of Ni3S2 affords articles such as fluid conduits and machine components with exceptional scale and corrosion resistance.

This disclosure relates to protective coatings useful in corrosive andscale forming environments. In particular, this disclosure relates toequipment comprising such scale and corrosion resistant coatings andmethods of producing such equipment.

BACKGROUND

Fluid conduits and other equipment used in the oil and gas industry arefrequently subjected to harsh conditions under which the conduits andequipment may undergo significant operational degradation as a result ofcorrosion and scaling of surfaces in contact with a production fluid. Inoil and gas wells in which the production fluid is rich in hydrogensulfide, corrosive scaling can be particularly severe. For example,production tubing may become rapidly clogged with iron sulfide scaleunder sour gas conditions wherein moderate to high concentrations ofhydrogen sulfide and carbon dioxide are in contact with productiontubing surfaces at temperatures and pressures prevailing in the downholeenvironment. Such clogging due to scale formation limits theproductivity of the well and, in some instances, forces the well to beshut down. Preventing the formation of scale extends the useful life andproductivity of the well.

Despite significant enhancements in the scaling and corrosion resistanceof fluid conduits and equipment used in the oil and gas industry,further improvements are needed. This disclosure provides details ofnovel and robust coating systems having outstanding scale and corrosionresistance, and which are suitable for use in a wide variety ofapplications in which corrosion and scale formation present operationalchallenges.

BRIEF DESCRIPTION

In a first set of embodiments, the present invention provides a fluidconduit, the fluid conduit defining an interior volume and comprising(a) a fluid conduit exterior surface; (b) a fluid conduit interiorsurface; (c) an electroless nickel protective coating disposed upon atleast one of the fluid conduit interior surface and the fluid conduitexterior surface; and (d) a layer of Ni₃S₂ disposed upon andsubstantially covering the electroless nickel protective coating.

In a second set of embodiments the present invention provides ahydrocarbon production tube defining a flow channel and comprising (a) atube exterior surface; (b) a tube interior surface; (c) an electrolessnickel protective coating disposed upon at least one of the tubeinterior surface and the tube exterior surface; and (d) a layer of Ni₃S₂disposed upon and substantially covering the electroless nickelprotective coating.

In a third set of embodiments the present invention provides a method ofproducing a fluid conduit comprising a nickel sulfide protective layer,the method comprising: (a) heating a fluid conduit comprising anelectroless nickel protective coating disposed upon a surface of thefluid conduit in contact with a fluid comprising hydrogen sulfide; and(b) depositing a protective layer of Ni₃S₂ upon and substantiallycovering the electroless nickel protective coating.

In a fourth set of embodiments, the present invention provides a machinecomponent comprising at least one surface having a protective outerlayer, the protective outer layer comprising: (a) an inner electrolessnickel coating; and (b) a layer of Ni₃S₂ disposed upon and substantiallycovering the electroless nickel coating.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Various features, aspects, and advantages of the present invention willbecome better understood when the following detailed description is readwith reference to the accompanying drawings in which like characters mayrepresent like parts throughout the drawings. Unless otherwiseindicated, the drawings provided herein are meant to illustrate keyinventive features of the invention. These key inventive features arebelieved to be applicable in a wide variety of systems which comprisingone or more embodiments of the invention. As such, the drawings are notmeant to include all conventional features known by those of ordinaryskill in the art to be required for the practice of the invention.

FIG. 1 illustrates a fluid conduit according to one or more embodimentsof the present invention.

FIG. 2 illustrates a fluid conduit according to one or more embodimentsof the present invention.

FIG. 3 illustrates a machine component according to one or moreembodiments of the present invention.

FIG. 4 is a scanning electron micrograph of a coating prepared accordingto one or more embodiments of the present invention.

FIG. 5 is a scanning electron micrograph of a coating prepared accordingto one or more embodiments of the present invention.

FIG. 6 is a scanning electron micrograph of a coating prepared accordingto one or more embodiments of the present invention.

DETAILED DESCRIPTION

In the following specification and the claims, which follow, referencewill be made to a number of terms, which shall be defined to have thefollowing meanings.

The singular forms “a”, “an”, and “the” include plural referents unlessthe context clearly dictates otherwise.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about” and “substantially”, are not to be limited tothe precise value specified. In at least some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value. Here and throughout the specification andclaims, range limitations may be combined and/or interchanged, suchranges are identified and include all the sub-ranges contained thereinunless context or language indicates otherwise.

As noted, in one or more embodiments the present invention provides acorrosion and scale resistant fluid conduit comprising at least onesurface having an electroless nickel (EN) protective coating disposedthereon. A layer of Ni₃S₂, at times herein referred to as Heazlewoodite,is disposed upon and substantially covers the electroless nickelprotective coating. The inventors have discovered that nearly all ENprotective coatings surprisingly undergo reaction with hydrogen sulfideat moderate temperature and high pressure to form a layer of scaleresistant Heazlewoodite on the surface of the EN protective coatinginitially in contact with a fluid containing hydrogen sulfide. Uponexposure of the EN protective coating to hydrogen sulfide at moderatetemperature and high pressure, nickel within the EN protective coatingis converted to Ni₃S₂ at or near the surface of the EN coating. The ENcoating is thus consumed to some degree during the formation of theNi₃S₂ layer. As more nickel reacts with hydrogen sulfide to form Ni₃S₂,the EN coating becomes substantially covered with Ni₃S₂ and, as aresult, encounters between hydrogen sulfide and nickel atoms present inthe EN coating are reduced over time and growth of the Ni₃S₂ layer slowsand eventually ceases. Provided the EN coating is of sufficientthickness at the outset of exposure to hydrogen sulfide, the productresulting from such exposure at moderate temperature and pressure willbe a layer of Heazlewoodite disposed upon and substantially covering theunconsumed portion of the underlying EN protective layer. Under suchcircumstances, the unconsumed portion of the underlying EN protectivelayer is hermetically isolated from contact with the environmentprovided the structural integrity of the layer of Heazlewoodite ismaintained. Example 1b (coupon 1b) in the Experimental Section of thisdisclosure is illustrative. Of the initial 1 mil (25.4 microns) thickhigh phosphorous EN protective coating, 25 microns of the originalnickel-phosphorous coating remain following reaction with hydrogensulfide in the presence of brine at 160° C. at a pressure of 2000-3000psi and deposition of a 10-micron thick Ni₃S₂ overlayer. The Ni₃S₂overlayer was determined to cover 100% of the outer surface of theunconsumed portion of the underlying EN protective coating andhermetically isolates it from further contact with brine and hydrogensulfide.

The Ni₃S₂ overlayer so produced exhibits outstanding scale resistance asis demonstrated experimentally herein. For example, iron sulfide scaleFeS (Mackinawite), formed by corrosion of an iron source in the presenceof hydrogen sulfide, does not adhere to the Ni₃S₂ overlayer. Moreover,the Ni₃S₂ overlayer is shown to be structurally robust and survives bothcontinuous rotation through brine solution at 300 rpm at 160° C. andhigh pressure, and explosive decompression test conditions. It isbelieved that the Ni₃S₂ overlayer will likewise be resistant to othertypes of scale formation, for example for example the formation ofscales comprising calcium carbonate (calcite), barium sulfate, (barite),magnesium carbonate, magnesium sulfate, calcium minerals, iron minerals,silica, dolomite, calcium sulfate, iron carbonate, Fe₂O₃, Fe₃O₄(magnetite), FeS₂ (iron pyrite), Fe₇S₈ (pyrrhotite), alpha FeOOH,Fe₂(OH)₃Cl, beta-FeOOH, and the like.

In one or more embodiments, the Ni₃S₂ overlayer is characterized by anaverage thickness in a range from about 0.5 to about 100 microns. In oneor more alternate embodiments, the Ni₃S₂ overlayer is characterized byan average thickness in a range from about 1 to about 20 microns. In yetanother set of embodiments, the Ni₃S₂ overlayer is characterized by anaverage thickness in a range from about 1 to about 10 microns.

The Ni₃S₂ overlayer has been observed by the inventors to form invarious morphologies depending on the nature of the initial ENprotective coating and/or the conditions under which the Ni₃S₂ overlayeris formed. Thus, the Ni₃S₂ overlayer formed by reaction of a portion ofa 1 micron thick high phosphorous electroless nickel coating exhibits ablocky crystalline morphology after prolonged exposure to hydrogensulfide and brine at moderate temperature and high pressure (See Coupons1a and 1b, Tables 1 and 2). Contrast this with the rod shapedcrystalline morphology of the Ni₃S₂ overlayer observed when an initial2-micron thick high phosphorous electroless nickel coating is exposed tohydrogen sulfide for a shorter period of time (16 hours) at moderatetemperature and pressure (See Coupons 2a and 2b, Tables 1 and 2). Theinventors have observed experimentally the formation of Ni₃S₂ overlayershaving nanowire morphologies, rod-like morphologies and block-likemorphologies; and believe that other Heazlewoodite morphologies such asnanosheet morphologies may be formed as well. In addition, combinationsof two or more of such morphologies may be present in a given Ni₃S₂overlayer. Further, it is believed that higher energy Ni₃S₂ morphologiesmay be converted to more stable forms upon prolonged heating, forexample. Thus, in one or more embodiments, the overlayer of Ni₃S₂ ischaracterized by one or more morphologies selected from the groupconsisting of one or more nanosheet morphologies, one or more nanowiremorphologies, one or more rod-like morphologies, one or more block-likemorphologies, and combinations of two or more of the foregoingmorphologies. Ni₃S₂ overlayer morphologies were determined by x-raydiffraction (XRD) and scanning electron microscopy. In one or moreembodiments, the Ni₃S₂ layer is initially formed with a nanowiremorphology which is transformed under the reaction conditions first to arod-like morphology and finally to a block-like morphology

The EN protective coating may contain one or more of a high phosphorouselectroless nickel coating, defined as containing from 10 to 20 percentby weight phosphorous based on the total weight of the coating; a midphosphorous electroless nickel coating, defined as containing from 8 to9 percent by weight phosphorous based on the total weight of thecoating; and a low phosphorous electroless nickel coating, defined ascontaining less than 8 percent by weight phosphorous based on the totalweight of the coating. In one or more embodiments, the EN protectivecoating is a multilayer coating comprising one or more high phosphorouselectroless nickel coatings, one or more mid phosphorous electrolessnickel coatings, one or more low phosphorous electroless nickelcoatings, or a combination of two or more of the foregoing high, mid andlow phosphorous EN coatings. In one or more embodiments, the ENprotective coating comprises at least one EN coating devoid ofphosphorous (See for example, coupon 3a of Table 1 in which the ENprotective coating is a bi-layer comprising an outer electroless nickelboron outer layer essentially free of phosphorous and a high phosphorouselectroless nickel inner layer in direct contact with the T95 steelsubstrate. It should be noted that the heat treatment referred to inExample 3 (coupon 3a), 350° C. for 1 hour, may have resulted inmigration of phosphorous into the electroless nickel boron outer layer,and conversely migration of boron into the electroless nickelphosphorous inner layer. Such heat treatment may also result in ametallurgical bond being formed between an EN inner layer and thesubstrate. Such a metallurgically bound layer is at times hereinreferred to as a bond layer. Multilayer EN protective coatings may beprepared stepwise, for example by coating the substrate first with aphosphorous-containing EN coating and subsequently subjecting the ENcoated substrate to a second electroless nickel coating step. Those ofordinary skill in the art will understand that phosphorous-containing ENprotective coatings may be prepared by reduction of dissolved nickelions with a phosphorous-containing reducing agent such as sodiumhypophosphite (NaPO₂H₂) in the presence of a substrate immersed in amedium comprising the dissolved nickel ions and thephosphorous-containing reducing agent. By substituting aboron-containing reducing agent, for example diborane (B₂H₆), for thephosphorous-containing reducing agent an EN protective coatingcontaining boron instead of phosphorous may be obtained.

In one or more embodiments, the EN protective coating comprises solidparticles enhancing one or more performance characteristics of such ENcoating. For example, the EN protective coating may contain hardparticles (nanoparticulate and larger) such as diamond, silicon carbide,cubic boron nitride, talc silica, alumina, and combinations thereofwhich enhance abrasion resistance. Alternatively, the EN protectivecoating may contain soft particles such as polytetrafluoroethylene(PTFE) particles and carbon black particles which enhance resistance todamage caused by movement of a coated surface of a first machinecomponent such as an impeller blade in close proximity to a surface of asecond machine component such as a housing. In multi-layer EN protectivecoatings the particles; hard, soft or a combination thereof, areadvantageously present in the outermost EN coating, for example as shownin FIG. 2 of this disclosure. In one or more embodiments, the ENprotective coating comprises solid particles in a range from about 10 toabout 40 percent by weight based on the total weight of the particularEN coating containing such particles. In an alternate set ofembodiments, the EN protective coating comprises solid particles in arange from about 10 to about 25 percent by weight based on the totalweight of the particular EN coating containing such particles. In yetanother set of embodiments, the EN protective layer comprises solidparticles in a range from about 10 to about 15 percent by weight basedon the total weight of the particular EN coating containing suchparticles. It should be noted that the presence in the EN protectivecoating of soft particulates such as PTFE or hard but heat sensitiveparticles may limit the maximum temperature at which a particular ENprotective coating may be subjected during heat treatment. For example,the structural integrity and/or performance characteristics of ENprotective coatings comprising PTFE particles may be compromised ifsubjected to a heat treatment protocol exceeding about 250° C. owing todecomposition of the PTFE within the EN matrix.

Fluid conduits provided by the present invention and comprising (a) afluid conduit exterior surface; (b) a fluid conduit interior surface;(c) an electroless nickel protective coating disposed upon at least oneof the fluid conduit interior surface and the fluid conduit exteriorsurface; and (d) a layer of Ni₃S₂ disposed upon and substantiallycovering the electroless nickel protective coating, include useful itemssuch as conduits for transporting fluids in the oil and gas industry,for example tubing used in downhole tubular applications in hydrocarbonproduction wells. In addition to downhole tubing used in hydrocarbonproduction, conduits provided by the present invention include any sortof structure though which a fluid may be caused to pass, includingwithout limitation, valves, manifolds, blowout preventers, Christmastrees, wellheads, surface pipelines, subsea pipelines, exhaust gas flowlines, cyclonic separators, liquid-liquid separators, and the like. Insome embodiments, the fluid conduit is a storage vessel. Storage vesselsqualify as fluid conduits in the sense that fluids flow into and out ofstorage vessels. In another embodiment, the fluid conduit is acontinuous reactor.

In one embodiment, the present invention provides a method of producinga fluid conduit comprising a corrosion and scale resistant nickelsulfide protective layer, the method comprising: (a) heating a fluidconduit comprising an electroless nickel protective coating disposedupon a surface of the fluid conduit in contact with a fluid comprisinghydrogen sulfide; and (b) depositing a protective layer of Ni₃S₂ uponand substantially covering the electroless nickel protective coating.Contact between the electroless nickel protective coating and hydrogensulfide is carried out at moderate temperatures and moderate to highpressures; the temperature being in one or more embodiments,temperatures in a range from about 100° C. to about 400° C., and thepressure being one or more pressures in a range from about 500 to about3000 psi. In one or more embodiments, contact between the electrolessnickel protective coating and hydrogen sulfide is carried out in thepresence of an aqueous solution comprising one or more dissolved saltssuch as sodium chloride, potassium bromide, lithium iodide, calciumchloride, calcium bromide, and combinations of two or more of theforegoing salts. In one or more embodiments, contact between theelectroless nickel protective coating and hydrogen sulfide mayadvantageously be carried out in the presence of one or more proticacids, such as hydrogen chloride, hydrogen bromide, hydrogen iodide,formic acid, and acetic acid. In one or more embodiments, an exogenousprotic acid is employed.

Turning now to the figures, FIG. 1 illustrates a fluid conduit 10according to one or more embodiments of the present invention. In one ormore embodiments, the fluid conduit 10 is a hydrocarbon production tubeshown in cross section. Fluid conduit 10 defines an interior volume 12,at times herein referred to as a fluid flow path, through which a fluidmay be caused to pass, and comprises a fluid conduit exterior surface 14and interior surface 16 which together define the thickness the fluidconduit wall bounded by surfaces 14 and 16. An electroless nickelprotective coating 18 is disposed on the fluid conduit interior surface16. In one or more embodiments, a metallurgical bond (not shown) isformed between the electroless nickel protective coating and the fluidconduit interior surface. A layer 20 of Ni₃S₂, also known asHeazlewoodite, is disposed upon and substantially covers the electrolessnickel protective coating 18. As used herein, the terms “substantiallycovers” and “substantially covering” in reference to the Ni₃S₂ layer andadjacent electroless nickel protective coating means that at least 80percent of the surface area of the electroless nickel protective coatingis covered by Ni₃S₂. In one or more embodiments, at least 95 percent ofthe surface area of the electroless nickel protective coating is coveredby Ni₃S₂. In an alternate set of embodiments, at least 99 percent of thesurface area of the electroless nickel protective coating is covered byNi₃S₂.

Referring to FIG. 2, the figure shows a fluid conduit 10 according toone or more embodiments of the present invention. The figure mayrepresent, for example, a hydrocarbon production tube, a fluid conduitdefining a fluid flow path within a compressor, a fluid conduit defininga fluid flow path within a gas-liquid separator, a fluid conduitdefining a flow path within a valve, and like fluid conduits. In theembodiment shown, the electroless nickel protective coating isconfigured as a bilayer coating comprising an inner electroless nickelbond layer 22 comprising from about 10 to about 20% by weightphosphorous based on a total weight of the electroless nickel bondlayer, and an electroless nickel outer layer 24 comprising hardparticles 26 selected from the group consisting of diamond, siliconcarbide, boron nitride, talc, and combinations of two or more of theforegoing hard particle types. A layer 20 of Ni₃S₂ substantially coversand hermetically seals electroless nickel outer layer 24 from fluidcontact with the interior volume 12 defined by the fluid conduit.

Referring to FIG. 3, the figure represents a machine component 30according to one or more embodiments of the present invention. Thefigure may represent, for example, an impeller blade, a compressorblade, an expander blade, a baffle, a diffuser within a fluid pump, avalve gate, and like machine components. During operation, machinecomponent 30 may be disposed within a fluid conduit provided by thepresent invention, for example a fluid conduit defining a fluid flowpath within a compressor, a fluid conduit defining a fluid flow pathwithin a gas-liquid separator, a fluid conduit defining a flow pathwithin a valve, and like fluid conduits. In the embodiment shown, aprotective outer layer 32 is disposed upon the machine component surface34. The protective outer layer 32 comprises an inner electroless nickelcoating 18, and a layer 20 of Ni₃S₂ disposed upon and substantiallycovering the electroless nickel coating. In one or more embodiments, thelayer of Ni₃S₂ hermetically seals the electroless nickel coating 18 fromfluid contact with the environment. In one or more embodiments, theelectroless nickel coating 18 hermetically seals the machine componentsurface 34 from fluid contact with the environment, as in the casewherein at least a portion of the electroless nickel coating 18 remainsin fluid contact with the environment following deposition of the layer20 of Ni₃S₂.

Referring to FIG. 4, the figure presents scanning electron micrographsshowing the typical appearance of electroless nickel phosphorous-coated(ENP-coated) test coupon surface before and after exposure to hydrogensulfide (See Experimental Part, Example 1a/1b, Tables 1 and 2). In theembodiment shown, are 2000× and 10000× magnification SEM images ofENP-coated test coupon 1a (Table 1) before exposure to hydrogen sulfideand ENP/Ni₃S₂ test coupon 1b (Table 2) after exposure to hydrogensulfide at moderate temperature and high pressure. The SEM images oftest coupon 1a show the smooth electroless nickel coating 18 coveringessentially all of the coupon surface. ENP/Ni₃S₂-coated test coupon 1bshows a deposit of Ni₃S₂ covering essentially all of the ENP coating.Note that lighter colored surface deposits 40 have been identified byXRD and EDS as Mackinawite (FeS) and are shown experimentally herein torepresent FeS formed by corrosive scaling of an uncoated T95 steelcontrol coupon and deposition upon the Ni₃S₂ surface coating of testcoupon 1b. In FIG. 4 and elsewhere herein, the Heazlewoodite (Ni₃S₂)layer 20 can be clearly seen to be a conformal, micro- ornano-crystalline coating with low affinity for FeS. The Ni₃S₂ layer 20has been found to adhere tenaciously to the underlying electrolessnickel coating 18.

Referring to FIG. 5, the figure presents scanning electron micrographsshowing a second ENP-coated test coupon surface before and afterexposure to hydrogen sulfide (See Experimental Part, Example 2a/2b,Tables 1 and 2). In the embodiment shown, 2000× and 10000× magnificationSEM images of ENP-coated test coupon 2a (Table 1) before exposure tohydrogen sulfide and ENP/Ni₃S₂-coated test coupon 2b (Table 2) afterexposure to hydrogen sulfide at moderate temperature and high pressure.The SEM images of test coupon 2a show the smooth electroless nickelcoating 18 covering essentially all of the coupon surface.ENP/Ni₃S₂-coated test coupon 2b shows a deposit of Ni₃S₂ coveringessentially all of the ENP coating. Again, lighter colored surfacedeposits 40 were identified by XRD and EDS as Mackinawite (FeS) derivedfrom the unprotected control coupon present during exposure to hydrogensulfide. Again, the Heazlewoodite (Ni₃S₂) layer 20 can be clearly seento be conformal with the surface of the underlying electroless nickelcoating 18. Moreover, layer 20 shows low affinity for FeS. Whenresubjected to the hydrogen sulfide-brine test protocol detailed in theExperimental Part herein, the Ni₃S₂ grains were shown by SEM to coarsenand grow in size while retaining low affinity for iron sulfide scale 40.Repetition of the hydrogen sulfide-brine test protocol a third andfourth time showed minimal further growth of the Ni₃S₂ grains, while thequantity of visible FeS surface deposits appeared to have decreased.This suggests that, as the Ni₃S₂ consolidates, it becomes moreanti-stick with respect to FeS deposition.

Referring to FIG. 6, the figure presents scanning electron micrographsshowing an eletcroless nickel boron coating (ENB coating) disposed upona high phosphorous electroless nickel bond layer (not visible in themicrograph) before and after exposure to hydrogen sulfide (SeeExperimental Part, Example 3a/3b, Tables 1 and 2). The overlayer 20 ofNi₃S₂ which formed on the surface of outer ENB coating was particularlyanti-stick with respect to FeS scale. This observation is consistentwith it being one of the more hydrophobic coatings prepared during thecourse of this study, as was established by contact angle measurements.While not wishing to be bound by theory, it is thought that the enhancedhydrophobicity of the Ni₃S₂ layer results from the nano-nodularmicrostructure of the surface, which makes it difficult for FeS depositsto achieve sufficient contact with the surface to adhere. Thenano-nodular microstructure of the EN coating 18 observed in test coupon3a, is reproduced in test coupon 3b following exposure to the hydrogensulfide-brine test protocol described in the Experimental Part as aresult of the fine microstructure of the Ni₃S₂ overlayer 40. It isnoteworthy that, as in the case of ENP coatings, nanocrystalline Ni₃S₂grows on the ENB surface, however, it grows with a finer microstructurethan Ni₃S₂ grown on the ENP coatings. The Ni₃S₂ layer appears to behighly conformal to underlying nano-nodular ENB surface, indicating goodadhesion between the ENB and Ni₃S₂ layer.

Experimental Part General Methods

Test coupons had dimensions of 2.87 inches by 0.87 inches by 0.125inches and were made of T95 steel. Electroless nickel coatings wereapplied by a commercial vendor, Surface Technology, Inc. RobbinsvilleN.J. 08691.

Representative coated test coupons are illustrated by entries 1a-7a,11a-12a, 15a and 26a of Table 1. The test coupons were characterized andshown to be uniformly coated.

TABLE 1 Test Coupon Electroless Nickel Coatings Example/ ElectrolessNickel Coating Underlayer Outerlayer Heat Coupon Composition thicknessthickness treatment  1a Mono-layer: high phosphorous ENP⁽¹⁾ — 1 mil — 2a Mono-layer: high phosphorous ENP — 2 mil —  3a Bi-layer: ENB⁽²⁾ overhigh 1 mil 1 mil 350° C. phosphorous ENP  4a Bi-layer: Highphosphorous⁽³⁾ ENP + 1 mil 0.5 mil   250° C. 20-25% PTFE over highphosphorous ENP  5a Bi-Layer: High phosphorous ENP + 1 mil 1 mil —20-25% PTFE over high phosphorous ENP  6a Bi-Layer: Low phosphorous⁽⁴⁾ENP + 1 mil 1 mil — 10% cubic boron nitride over high phosphorous ENP 7a Bi-Layer: Low phosphorous ENP + 1 mil 1 mil 350° C. 10% cubic boronnitride over high phosphorous ENP 11a Bi-Layer: Mid phosphorous⁽⁵⁾ ENP +1 mil 4 mil 350° C. 10% Nano-Plate ™⁽⁶⁾ over high phosphorous ENP 12aBi-Layer: Low phosphorous ENP + 1 mil 1 mil 350° C. 35% CDC-2-HD⁽⁷⁾ overlow phosphorous ENP⁵ 15a Bi-Layer: Mid phosphorous ENP + 1 mil 4 mil350° C. 20% SiC⁽⁸⁾ over high phosphorous ENP 26a Mono-Layer: Lowphosphorous ENP + — 4 mil 350° C. 35% CDC-2-HD Key: ⁽¹⁾Electrolessnickel phosphorous. ⁽²⁾Electroless nickel boron. ⁽³⁾High phosphorous ENPcontains 10 to 20% by weight P. ⁽⁴⁾Low phosphorous ENP contains lessthan 8% by weight P ⁽⁵⁾Mid phosphorous ENP contains 8 to 9% by weight P.⁽⁶⁾Sub-micron nanoparticulate diamond available from Surface Technology,Inc. ⁽⁷⁾Micron scale diamond particles present in Composite DiamondCoating ™ available from Surface Technology, Inc. ⁽⁸⁾Silicon carbide.

In model scaling experiments test coupons were mounted on a rotatingcage apparatus and rotated at 300 rpm while in contact with a brinesolution within a heated autoclave pressurized with hydrogen sulfide andnitrogen gas. An uncoated T95 steel test coupon was placed in closeproximity to the electroless nickel-coated test coupons in order tomodel corrosive scale formation conditions in which the uncoated T-95steel test coupon serves as the iron source for FeS scale. Test couponswere weighed before and after being subjected to hours-long exposure tohydrogen sulfide and brine. All electroless nickel-coated test coupons(2a-7a, 11a, 12a and 26a) were observed to increase in weight or remainunchanged in weight (test coupons 1a and 15a) following the modelscaling experiments, and all uncoated T95 steel control coupons wereobserved to decrease in weight following the model scaling experiments.Further, the surface appearance of the electroless nickel-coated testcoupons was transformed from a lustrous reflective surface appearancecharacteristic of electroless nickel coatings, to a dull gray-greensurface appearance. The uncoated T-95 steel test coupons turned blackunder the test conditions.

Preparation of Heazlewoodite (Ni₃S₂) Coatings on ElectrolessNickel-Coated Substrate

Heazlewoodite (Ni₃S₂) coatings were unexpectedly formed on electrolessnickel coated substrates during corrosive scaling tests. The tests werecarried out in a one-liter C276 steel autoclave equipped with a purgetube and rotating cage apparatus on which were secured five electrolessnickel-coated test coupons (See Table 1) and an uncoated control couponmade of T95 steel. A 1 molar sodium chloride solution (500 mL), anamount sufficient to completely submerge all six coupons, was purgedcontinuously in a premixing unit with oxygen free nitrogen gas(99.9999%) over several hours at ambient temperature. The oxygen levelin the brine solution was monitored with CHEMetrics ULR CHEMets kitcapable of determining the concentration of dissolved oxygen in thebrine in a range from about 0 to about 20 parts per billion (ppb). Inrepresentative experiments the brine was considered strictly anoxic whenthe concentration of dissolved oxygen was less than 4 ppb. Once thebrine was judged to be strictly anoxic it was transferred to theautoclave under a nitrogen atmosphere. A mixture of hydrogen sulfide andnitrogen gas at atmospheric pressure and ambient temperature (4% H₂S inN₂) (2.0 liters, approximately 100 milligrams of H₂S) was introducedinto the autoclave bringing the initial pressure in the autoclave to 55psi. The pressure inside the autoclave was boosted to 1450-1500 psiusing a high pressure pump to introduce additional nitrogen gas. Theautoclave was then heated at 160° C. at a pressure of 2250-2370 psi forapproximately 16 hours while rotating the rotating cage at 300 rpm. Theautoclave was allowed to cool to ambient temperature and was ventedthrough a H₂S scrubber and purged with nitrogen. The test coupons wererinsed with deionized water, dried and characterized variously by weightgain, explosive decompression testing, X-ray powder diffraction (XRD)and electron microscopy. Representative Ni₃S₂ coated test coupons areillustrated by entries 1b-7b, 11b-12b, 15b and 26b of Table 2.

TABLE 2 Electroless Nickel Coatings with Ni₃S₂ Outer Layer Ni₃S₂Example/ layer Ni₃S₂ layer Ni₃S₂ % Scale % Mass Coupon thicknessmorphology Coverage Resistance Gain  1b 0.5-1.0 Blocky 100% good 0.0microns crystals  2b⁽¹⁾ 1-2 Rod shaped 100% good 0.0147 micron⁽²⁾crystals  3b NA⁽³⁾ NA⁽³⁾ 100% good 0.018  4b NA⁽³⁾ NA⁽³⁾ NA⁽³⁾ Very good0.0927  5b NA⁽³⁾ NA⁽³⁾ NA⁽³⁾ Very good 0.051  6b NA⁽³⁾ NA⁽³⁾ NA⁽³⁾ Verygood 0.0613  7b NA⁽³⁾ NA⁽³⁾ NA⁽³⁾ good 0.156 11b NA⁽³⁾ NA⁽³⁾ NA⁽³⁾ Verygood 0.0601 12b⁽⁴⁾ 10 micron Blocky, with 100% Very good 0.0563 someembedded diamond 15b⁽⁵⁾ 10 micron Continuous, 100% Very Good blocky,mixed with SiC crystals 26b⁽⁶⁾ 10 micron Continuous  50% Very good0.0395 with exposed diamond particle surfaces Key: ⁽¹⁾Single 16 hourcycle as described above but with higher initial H₂S pressure (100 psiversus 55 psi). ⁽²⁾Ni₃S₂ layer passed explosive decompression test.⁽³⁾Not Ascertained ⁽⁴⁾Two 16 hour cycles with initial H₂S pressure of 55psi. ⁽⁵⁾Prolonged exposure to hydrogen sulfide-brine protocol. ⁽⁶⁾Single16 hour cycle as described above but with higher initial H₂S pressure(100 psi versus 55 psi), higher brine concentration (3 molar) and theaddition of a source of soluble Fe²⁺ ions.

The electroless nickel-Ni₃S₂ coated coupons were observed to haveexcellent resistance to scale adhesion on the outer Ni₃S₂ layer which innearly all instances covered essentially 100% of the outer surface testcoupon. In one instance, test coupon 26a was observed to provide a Ni₃S₂coating covering only about 50% of the surface of the test coupon. Thiswas thought to be due to the relatively high concentration of diamondparticles in the original electroless nickel mono-layer. Notwithstandingthe partial covering observed for test coupon 26b, the Ni₃S₂ outer layerexhibited very good resistance to scale accretion. The exposed diamondparticle surfaces at the outer surface of the Ni₃S₂ layer wereapparently non-stick with respect to FeS scale as well.

The experimental results indicate that the thickness of theHeazlewoodite layer may be limited to about 10 microns. Thus, coupon 1bhaving an initial layer of Ni₃S₂ having a thickness between about 0.5and 1.0 microns thick, was subjected to extended exposure to hydrogensulfide and brine over a twenty-one day period during which the Ni₃S₂layer grew in thickness to about 10 microns. Of the initial 1 mil (25.4microns) thick high phosphorous ENP layer, 25 microns of anickel-phosphorous layer remained following deposition of the Ni₃S₂overlayer. Coupons 12b, 15b, and 26b comprised Ni₃S₂ layers about 10microns thick. Thus it appears that longer reaction times and/or higherconcentrations of hydrogen sulfide did not result in Ni₃S₂ coatingshaving thicknesses greater than 10 microns.

Method 1: Preparation of Heazlewoodite (Ni₃S₂) Coating on an ElectrolessNickel-Coated Hydrocarbon Production Tube

A hydrocarbon production tube approximately 30 feet in length, threadedat both ends, having an outer diameter of approximately 4.5 inches andhaving inner and outer surfaces is first coated with the electrolessnickel coating composition of Example 1a of Table 1 of this disclosureon the inner surface of the tube to a thickness of approximately 2 mil.As noted, such electroless nickel coatings may be applied by commercialapplicators such as Surface Technology, Inc. of Robbinsville, N.J. Afirst end of the tube is sealed with a first threaded steel cap likewisecoated with 2 mil of the high phosphorous ENP coating of Example 1a. Thetube is then moved into a vertical position open end up. Sufficient 1molar sodium chloride brine solution to fill approximately threequarters of the length of the tube is added to the tube through the openend. The open end of the tube is then sealed with a second threadedsteel cap, likewise coated with 2 mil of the high phosphorous ENPcoating of Example 1a. The second threaded steel cap is equipped withgas inlet and gas outlet ports. The headspace within the tube is purgedwith nitrogen at atmospheric pressure and then pressurized with 4%hydrogen sulfide in nitrogen gas mixture to 1400 psi. The tube is theninserted horizontally into an oven equipped with roller bearings whichallow the tube to be rotated at approximately 60 rpm. The oven is sizedsuch that the entire length of the tube may be heated during a singleheating cycle without moving the tube horizontally through the oven atany point during the heating cycle. The oven temperature is raised toapproximately 160° C. and heated at that temperature for 24 hours whilerotating the tube at 60 rpm. The tube is allowed to cool and is ventedthrough a hydrogen sulfide scrubber while purging with nitrogen gas. Thebrine solution is recovered for reuse and the tube is rinsed inside andout with fresh water and allowed to dry. The product hydrocarbonproduction tube comprises an electroless nickel protective coatingdisposed upon the interior surface of the tube and a layer of Ni₃S₂disposed upon and substantially covering the electroless nickelprotective coating.

Method 2: Preparation of Heazlewoodite (Ni₃S₂) Coating on an ElectrolessNickel-Coated Hydrocarbon Production Tube Under Strictly AnoxicConditions

The method is essentially the same as Method 1 herein with the exceptionthat the brine solution is thoroughly deoxygenated prior to addition ofthe brine to the tube, and such addition is carried out under a strictlyanoxic atmosphere. A source of ferrous ions (ferrous chloride) is added,again under strictly anoxic conditions. The open end of the tube is thensealed with a second threaded steel cap, likewise coated with 2 mil ofthe high phosphorous ENP coating of Example 1a. The second threadedsteel cap is equipped with gas inlet and gas outlet ports. The headspacewithin the tube is purged with nitrogen at atmospheric pressure and thenpressurized with 4% hydrogen sulfide in nitrogen gas mixture to 1400psi. The tube is then inserted horizontally into an oven equipped withroller bearings which allow the tube to be rotated at approximately 60rpm. The oven is sized such that the entire length of the tube may beheated during a single heating cycle without moving the tubehorizontally through the oven at any point during the heating cycle. Theoven temperature is raised to approximately 160° C. and heated at thattemperature for 24 hours while rotating the tube at 60 rpm. The tube isallowed to cool and is vented through a hydrogen sulfide scrubber whilepurging with nitrogen gas. The brine solution is recovered for reuse andthe tube is rinsed inside and out with fresh water and allowed to dry.The product hydrocarbon production tube comprises an electroless nickelprotective coating disposed upon the interior surface of the tube and alayer of Ni₃S₂ disposed upon and substantially covering the electrolessnickel protective coating.

The foregoing examples are merely illustrative, serving to illustrateonly some of the features of the invention. The appended claims areintended to claim the invention as broadly as it has been conceived andthe examples herein presented are illustrative of selected embodimentsfrom a manifold of all possible embodiments. Accordingly, it isApplicants' intention that the appended claims are not to be limited bythe choice of examples utilized to illustrate features of the presentinvention. As used in the claims, the word “comprises” and itsgrammatical variants logically also subtend and include phrases ofvarying and differing extent such as for example, but not limitedthereto, “consisting essentially of” and “consisting of” Wherenecessary, ranges have been supplied, those ranges are inclusive of allsub-ranges there between. It is to be expected that variations in theseranges will suggest themselves to a practitioner having ordinary skillin the art and where not already dedicated to the public, thosevariations should where possible be construed to be covered by theappended claims. It is also anticipated that advances in science andtechnology will make equivalents and substitutions possible that are notnow contemplated by reason of the imprecision of language and thesevariations should also be construed where possible to be covered by theappended claims.

1. A fluid conduit, the fluid conduit defining an interior volume andcomprising: (a) a fluid conduit exterior surface; (b) a fluid conduitinterior surface; (c) an electroless nickel protective coating disposedupon at least one of the fluid conduit interior surface and the fluidconduit exterior surface; and (d) a layer of Ni₃S₂ disposed upon andsubstantially covering the electroless nickel protective coating.
 2. Thefluid conduit according to claim 1, wherein the layer of Ni₃S₂ ischaracterized by an average thickness in a range from about 1 to about100 microns and hermetically isolates the electroless nickel protectivecoating from the fluid conduit interior volume.
 3. The fluid conduitaccording to claim 1, wherein the layer of Ni₃S₂ is characterized by oneor more morphologies selected from the group consisting of one or morenanosheet morphologies, one or more nanowire morphologies, one or morerod-like morphologies, one or more block-like morphologies, andcombinations of two or more of the foregoing morphologies.
 4. The fluidconduit according to claim 1, wherein the layer of Ni₃S₂ ischaracterized principally by one of i) one or more nanosheetmorphologies, ii) one or more nanowire morphologies, iii) one or morerod-like morphologies, and iv) one or more block-like morphologies. 5-7.(canceled)
 8. The fluid conduit according to claim 1, wherein theelectroless nickel protective coating is configured as a bilayer coatingcomprising an inner electroless nickel bond layer comprising from aboutto about 20% by weight phosphorous based on a total weight of theelectroless nickel bond layer, and an electroless nickel outer layercomprising hard particles selected from the group consisting of diamond,silicon carbide, boron nitride, talc, and combinations of two or more ofthe foregoing.
 9. The fluid conduit according to claim 8, wherein thehard particles are present in a range from about 10 to about 40 percentby weight based on the total weight of the electroless nickel outerlayer.
 10. The fluid conduit according to claim 1, wherein ametallurgical bond is formed between the fluid conduit interior surfaceand the electroless nickel protective coating.
 11. The fluid conduitaccording to claim 1, wherein the fluid conduit is selected from thegroup consisting of production tubing, valves, storage vessels, reactionvessels, surface pipelines, subsea pipelines, cyclonic separators,wellheads, manifolds, blowout preventers, Christmas trees, and exhaustgas conduits.
 12. The fluid conduit according to claim 1, wherein thefluid conduit is a tube for transporting a hydrocarbon production fluid.13-21. (canceled)
 22. A method of producing a fluid conduit comprising anickel sulfide protective layer, the method comprising: (a) heating afluid conduit comprising an electroless nickel protective coatingdisposed upon a surface of the fluid conduit in contact with a fluidcomprising hydrogen sulfide; and (b) depositing a protective layer ofNi₃S₂ upon and substantially covering the electroless nickel protectivecoating.
 23. The method of claim 22, wherein said heating is carried atone or more temperatures in a range from about 100 to about 400 degreescentigrade.
 24. The method according to claim 22, wherein the protectivelayer of Ni₃S₂ is characterized by an average thickness in a range fromabout 1 to about 100 microns and hermetically isolates the electrolessnickel protective coating.
 25. The method according to claim 22, whereinsaid fluid comprising hydrogen sulfide further comprises water.
 26. Themethod according to claim 22, further comprising a post depositionannealing step which converts an initial Ni₃S₂ morphology into analternate Ni₃S₂ morphology.
 27. A machine component comprising at leastone surface having a protective outer layer, the protective outer layercomprising: (a) an inner electroless nickel coating; and (b) a layer ofNi₃S₂ disposed upon and substantially covering the electroless nickelcoating.
 28. (canceled)
 29. The machine component according to claim 27,wherein the layer of Ni₃S₂ is characterized by one or more morphologiesselected from the group consisting of one or more nanosheetmorphologies, one or more nanowire morphologies, one or more rod-likemorphologies, one or more block-like morphologies, and combinations oftwo or more of the foregoing morphologies.
 30. The machine componentaccording to claim 27, wherein the layer of Ni₃S₂ is characterizedprincipally by one of i) one or more nanosheet morphologies, ii) one ormore nanowire morphologies, iii) one or more rod-like morphologies, andiv) one or more block-like morphologies. 31-33. (canceled)
 34. Themachine component according to claim 27, wherein the electroless nickelprotective coating is configured as a bilayer coating comprising aninner electroless nickel bond layer comprising from about 10 to about20% by weight phosphorous based on a total weight of the electrolessnickel bond layer, and an electroless nickel outer layer comprising hardparticles selected from the group consisting of diamond, siliconcarbide, boron nitride, talc, and combinations of two or more of theforegoing.
 35. The machine component according to claim 34, wherein thehard particles are present in a range from about 10 to about 40 percentby weight based on the total weight of the electroless nickel outerlayer.
 36. (canceled)
 37. The machine component according to claim 27,which component is a compressor blade, a turbine blade, a turboexpanderblade, a turbocharger vane, a diffuser vane, an inlet guide vane, anoutlet guide vane, a pump vane, a fane blade, a mixer blade, animpeller, a bearing, a bushing, a motor housing, a pump housing, acompressor housing, a shroud, a rotor, a stator, a driving rod, a strut,a gear box, a gear wheel, a piston, a piston rod, a spring, a cantileverarm, a seal, a rivet, a bolt, a nut, a washer, a screw, a dowel, or acombination of two or more of the foregoing machine components. 38.(canceled)